A short history of artificial light – a spectral point of view

In our modern environment, artificial light plays an important role, both in the expansion of human activities beyond the twilight and in the use of places with little or no natural light. However, despite deceptive appearances, the quality of artificial light is currently experiencing several substantial impoverishments which, consequently, reduce the quality of environments and spaces that it radiates.
Yet these invisible changes are essential since, apart from aesthetic considerations, the effects of light on our physiology are known and especially crucial for regulating our metabolism. But beyond the public health issues it is indeed a deterioration of space, of the architecture we live in that we are witnessing, without realizing it. It is a forced sensory deprivation, the vanishing of whole sections of the visible, the disappearance of a part of reality.
Our point here is not to question the direction of progress, nor to let us go to easy but sterile nostalgia, but rather to carefully analyze these industrial developments in order to create new spaces that reflect the invisible characteristics and impalpable alterations in our artificial light environment.

"The European Union has set the schedule for phasing out traditional light bulbs in Europe. Traditional bulbs will no longer be sold as of September 1, 2012. Traditional bulbs will be all replaced by so-called 'new generation' bulbs."
This measure, praiseworthy from an energy saving point of view (reduction of CO2 emissions of about 15 million tons per year), is not without a major and yet immaterial counterpart. The downside, besides the price of the so-called next-generation devices, is the quality of light. This assertion might sound trivial, since the essential characteristics in the description of the lighting of a place are usually the quantity and color, or rather the color temperature : a space with too much, or too little light ; a cold, industrial, or warm light. These are the only criteria that can be heard on artificial lighting (it should be noted here that these two points are however not to be neglected, we will return later).
However, there is a criterion that is nevertheless fundamental to appreciate the light, which is not directly perceptible and, precisely for this reason, is undergoing a unprecedented devaluation since its initial identification, from 1948 by scientist JP Bouma and its qualification by the International Commission on Illumination (CIE): the color rendering index, often abbreviated CRI, which depends more precisely on the spectral power distribution of a light. The CRI of a light describes his ability to reflect accurate color of a surface. Bouma noticed that daylight was much better to estimate the colors and the work of the CIE established its value to 100 to determine the scale of CRI. Thus, a light with high CRI, close to 100, can render the colors properly (homogeneity in the spectral power distribution), while a low CRI is synonymous with loss of color range, so a disappearance of colors.
Artificial lighting was born as primary fire and was domesticated through the use of controlled combustion of oil and other substances (candles, gas). The advent of artificial lighting in Europe took place with the arrival of gas in the eighteenth century, allowing widespread public lighting and completely changing the perception of the night.
Now, all these lighting techniques using combustion, despite a questionable cost-efficiency and often toxic fumes always had a CRI close to that of daylight, since the source is similar to a "black body" (physics concept wherein the electromagnetic emission is directly related to the temperature). Of course, the small amount of scattered light and its particular reddish color temperature (as derived from the infrared) have always left thinking that the quality of these lights was low and distorted reality. And this is indeed the case to some extent : the predominance of higher wavelengths (red) does not allow to easily discern with the naked eye shades of blue or purple.
It was not until the arrival of the incandescent light bulb by J. Bowman Lindsay, developed by Thomas Edison, for the nostalgic to declare this new source as the ultimate worsening of light, regretting the warm glow of gaslights and their tangible dimension by the inhalation of combustion products. However, the incandescent lamp represented enormous progress on a functional point of view (providing light without moving fuel, stability, no emission, etc...) without sacrificing quality. Rather, incandescent lamps promised a pretty good rendering, still very warm but variable color temperatures, and had above all a very high CRI, once again comparable to that of daylight. To summarize, the magnitude and consistency of the light spectrum emitted by incandescent lamps allowed to return all shades of colors of nature, although again the predominance of red disrupted sometimes this perception.
However, science has developed in the twentieth century many other techniques to produce artificial light. In particular, research in chemistry gave an opportunity to test different gases to reduce wear and increase the brightness of filaments, and different powders to coat the interior side of bulbs, up to get rid of filament with the invention of high-pressure discharge lamps and especially fluorescent tubes (UV radiation emitted by the gas is converted into visible light by the coating of the tube. Moreover, the evolution of electronics has enabled the development of light emitting diodes, with an entirely different process but always subject to complex chemical assays to control the effects.
In the early twentieth century it was difficult to control the color of fluorescent tubes, and these are limited to commercial use because of the bright colors to which they are confined. Fluorescent lamp with much more complex systems, developed by Daniel Moore, however, allowed to get a white enough light and would gradually emerge thanks to their energy efficiency. Paradoxically, those first white fluorescent tubes were favored initially in special uses requiring to discern colors, precisely because of the weakness of incandescent lamps in shades of blue. One can imagine that for the first time in the history of mankind artificial light allowed to easily distinguish a purple from a turquoise. However, it was not until the 70s and major industrial developments for fluorescent tubes (improperly called "neon") to become widespread in everyday life, especially in large spaces requiring regular, significant and relatively neutral illumination (factories, offices, supermarkets, etc..).
Thus, this type of artificial light became a standard, a base for anyone who wants to illuminate a space at low cost. Extensive research conducted in its favor at the end of the twentieth century allowed – like with many other technologies – its substantial miniaturization, popularized under the name of compact fluorescent lamps or CFL (the "new generation" in question). The outstanding efficiency of the fluorescence associated with global environmental awareness had gradually got the better of incandescence lamp, at the expense of color quality. While the incandescence is not an ideal of neutrality in the representation of the visible spectrum, promoting largely low frequencies, yet it has the advantage not to omit slices of the visible – it just reduces them. Fluorescent light, despite progress, runs through peaks: it diffuses weakly a consistent basis, but most of its radiation is condensed in a few peaks of very specific colors, simply annihilating sections of color spectrum, regardless of any color temperature. Everyone has seen the wan impression that emerges from a scene illuminated with a low-end fluorescent tube (CRI of 60 for a tube rated 640 for example). It is not a problem of color temperature since some of these lamps have a warm and neutral light like the sun (640 or 840 classification means a color temperature of 4000K). Then it is the poor spectral power distribution, which, despite a CRI between 60 and 80%, omits in fact probably much color, forcing the human eye and brain to reconstruct a truncated real seen through this forced filter.
Thus, programmed substitution of traditional incandescent lamps with so-called "new generation" compact fluorescent lamps is producing a gradual shift of the nighttime perceptible real. Every house, every office, every public place where the diversity of lighting allowed a good visual appreciation of our environment is undergoing the same fate : after dusk, fringes of visible are silently selected without us knowing, some colors (most actually) disappear, the real is already slipping out.
That said, this angels' share, this invisible reality that disappears can be, with fluorescent lamps, known or at least estimated. Tubes CRI is clearly stipulated: generally between 60 and 80. Striking curves of spectral power distribution are also available from the manufacturers. This does not hold true for the next revolution that threatens the world of artificial light.
Light-emitting diodes - LED - will indeed make lighting fall over into a new chaos. LEDs are very simple and cheap to produce, and they are very energy-efficient. They can be grouped easily, and their explosion in recent years has led to a widespread use – beyond small electronic gadgets – to directly illuminate our built environments. The largest lighting manufacturers produce LED lamps, of all forms and of all types, whereas none of them actually produces the diode itself, the light source. LEDs are made somewhat randomly, mainly in China, and the bulbs that host them cannot really guarantee specific technical features. The white light lamps are either composed of a white LED, three blue-green-red LED, four colors LED or more. The CRI of these lamps are often incalculable: frequently close to 20, yet they give the impression to distinguish colors by increasing the contrast. With LEDs the evolution in time of the color temperature (and necessarily spectrum) is very important, totally random and therefore worrying. However, these lamps may soon, because of cost and performance, replace all other types of lamps.
Again, the issue here is not to gratuitously decry these technological advances, because if they bring their own problems, their development is necessarily linked to certain qualities (high performance and low power consumption, ease of implementation, duration of life) that we, architects can exploit.
One again the idea is rather to study, from an objective and scientific point of view, the spectral qualities of these various light sources on the one hand, and the reception of these lights in our eyes and our brain on the other hand, to optimize the use, or rather to optimize the architecture which is irradiated by these rays. If a lamp's CRI is low, it is then important to know under what wavelengths the light emit, what is its spectral power distribution, in order to create an architecture that reflects and even operates this particular quality.
An interesting example is that of the low-pressure sodium lamp (LPS). This basic system is extremely common because of its particularly high efficiency: it is thus used for the illumination of cities along the streets, roads and highways. Its characteristic color temperature gives this particular orangey shade to our nocturnal urban environment. However, these lamps have among the lowest CRI, close to 0. This means that the light is monochromatic, in a wavelength of 589.3 nm, and cannot render any other color. At night, along a road, we believe we can discern red from blue, but it is physically impossible with LPS light. A photo taken with such a light is monochromatic and necessarily, so to say, in black and white. Furthermore, for humans this wavelength is particularly suited to night vision, since the wavelengths around the blue (totally absent from LPS) induces a contraction of the pupil, limiting the amount of light perceived by the eye. After a few seconds of retina adaptation, the human brain rebalances the perceived color to produce a virtual spectrum, giving an impression of the scene as close as possible to objective reality. Now with LPS lighting, the brain has no other color to produce the virtual spectrum, so it literally produces a grayscale image.
So that becomes a space illuminated only in black and white? What is the most appropriate architecture, the one that operates at best this particular artificial light. It is known that LPS lighting makes police work more difficult on the road at night, as distinguishing the color of a car is impossible. But one could imagine very intensely lit places where it would not be useful to perceive colors, and where this feature of artificial lighting would be known and controlled. Similarly, low CRI fluorescent tubes lighting with such a particular spectral power distribution should be used for architecture that have been developed taking into account the quasi absence of most wavelengths and overabundance of certain colored peaks.

In the project Spectral Apartment, we sought to explore these features based on a bi-polar analysis of space. The project is a renovation of a small one-bedroom studio in the Paris suburbs. As the client was particularly concerned about the issue of lighting his apartment, on the first floor facing a courtyard, we have developed a reflection on the quality of artificial light as the basis of the architectural project. Thus, the first phase consisted of a sharing-out of program elements according to their spectral needs : which uses need a good color rendering, which spaces can be content with a very low color rendering? This first classification generates a hierarchy of space: on one side the kitchen, living room, dressing room where distinguishing colors is necessary, on the other hand the bed, toilet, shower where monochromatic light suffice.
This bipolarity between high and low CRI becomes the crucial element of space composition. Holding two separate light sources, a 2m high simple wall divides the studio and generates this composition. On the one hand an over 90 CRI lighting (940 fluorescent tubes) with a neutral color temperature (4000K), on the other hand a warm light from low-pressure sodium lamps with zero CRI. The accurate analysis of the distribution of light in space then indicates the positioning of uses. Since there is no other source of light in the studio those spaces are arranged in a form of open plan, only two transparent / translucent walls are occasionally placed for convenience when privacy is needed. As both sources can be switched independently, different lightning patterns appear, giving rise to other uses in particular areas of ​​the apartment.
The apartment is designed in a simple and neutral expression, without color or particular detail, annihilating any architectural expressiveness to leave only the logic of composition generated by light.